1. Field of the Invention
This invention relates to a printer for printing characters and images on recording paper and also to the ink sheet for use on a color thermal printer.
2. Prior Art
FIG. 1 is a perspective view of a conventional printer, in which 1 indicates a paper cassette for storing the recording paper, 2 shows the recording paper stored inside this paper cassette 1, 3 stands for a platen roller around which the recording paper 2 is wound at the time of the transfer of images for printing, 4 represents a clamper free to move in the direction R of the radius of the platen roller 3 mentioned above, 5 indicates a thermal printing head for transferring images onto the recording paper, and 6 marks a motor, the revolutions of which are transmitted from an output gear 7 mounted on the output shaft to a gear 8, then from a gear 9 mounted on the same shaft as this gear 8 to a gear 10 mounted on the rotating shaft 11 of the platen roller 3 mentioned above, and drive the platen roller 3 for its rotation. 12 represents the paper feeding roller which feeds the paper towards the platen roller 3, 13 stands for a paper discharging roller, which discharges the recording paper 2 upon the completion of the transfer of images thereto, 14 denotes an ink sheet stored inside an ink cassette not illustrated in the Figure, and the ink sheet has ink coated on a transparent film. 15 indicates a paper detecting sensor.
Next, the working of the printer is described with reference to FIG. 2 through FIG. 5. FIG. 2 illustrates the state for feeding the paper. The paper feeding roller 12 rotates in the direction as indicated by the arrow mark a in the Figure, thereby transporting the recording paper 2, which passes through the paper detecting sensor 15. In this process, the paper detecting sensor 15 detects the passage of the recording paper 2 and generates the signal as illustrated in FIG. 5. In approximately A seconds after this paper detecting sensor 15 generates the, signal, the recording paper 2 is inserted between the clamper 4 and the platen roller 3. The clamper 4 shifts its position to the point R.sub.1 in the direction towards the center of the platen roller 3 in the above-mentioned A seconds after this paper detecting sensor 15 generates the signal, and the platen roller 3 holds the recording paper 2, thrusting it under pressure against the platen roller 3. Subsequently, the motor 6 sets into its revolution, and its revolving motion is then transmitted to the platen roller 3 by way of a gear 7, a gear 8, a gear 9, and a gear 10, and, by the rotation of the platen roller 3 in the direction indicated by the arrow mark b, the recording paper 2 is wound around the outer circumference of the platen roller 3.
FIG. 3 illustrates the state of transferring images for their printing. An ink sheet 14 is thrust onto the recording paper 2 by means of the thermal printing head 5, and, while the platen roller 3 rotates in the direction indicated by the arrow mark b1 in the Figure, the thermal printing head 5 generates heat, by which the ink on the ink sheet 14 is sublimated and stuck to the recording paper. By executing this process for sticking the ink in this manner for each of the three colors, i.e. yellow, magenta, and cyan, the printing of images in color is performed on the recording paper 2. The printing of images in each of the colors is started from the moment when the photoelectric switch 16 shown in FIG. 3 detects the clamper 4.
Moreover, when the clamper 4 turns as it passes through the position of the thermal printing head 5, the thermal printing head 5 temporarily escapes upwards so that it will not interfere with the movement of the clamper 4.
FIG. 4 illustrates the state of the discharge of paper. After the color printing of images in three colors is completed, the platen roller 3 turns in reverse in the direction c shown in the Figure, the recording paper 2 being thereby guided to the paper discharging guide not illustrated in the Figure and being then discharged by the paper discharging roller not illustrated in the Figure.
Since the conventional printer is constructed as described hereinabove, it is conceivable, in case there occurs any slip between the paper feeding roller 12 and the recording paper 2, or there occurs any fluctuation in the rotation of the paper feeding roller 12, at the time when the paper is fed, that the recording paper 2 remains in the state not yet inserted between the clamper 4 and the platen roller 3 when the seconds A have elapsed after the paper detecting sensor 15 generates the signal. In this case, the clamper 4 is not able to thrust down the recording paper 2, and it may sometimes happen that the feeding of the paper is not performed in any proper way. In order to prevent such a situation as this, it is necessary to suppress the slipping between the paper feeding roller 12 and the recording paper 2 by suppressing the fluctuations in the rotation of the paper feeding roller 12. In consequence of this, it is required to attain a high degree of precision in the equipment, which in its turn pushes up the costs of the equipment to a high level. Furthermore, even by the use of a high-precision equipment, it is difficult to suppress the slipping between the paper feeding roller 12 and the recording paper 2. Consequently, the positional relation between the clamper 4 and the recording paper 2 while the clamper is holding down the recording paper 2 changes at each such time, with the result the conventional printer is liable to cause the problem that the position of the printed area in relation to the recording paper 2 will fluctuate.
FIG. 6 through FIG. 9 illustrate another conventional printer. In these Figures, 101 represents the recording paper for printing the information, 102 indicates the paper feeding roller for feeding the recording paper 101, 103 stands for the paper discharging roller for discharging the recording paper 101, 104 denotes the paper guide, 105 indicates the platen roller around which the recording paper 101 is wound, 106 marks the clamper which has an oblong hole 161 into which the protrusion 151 provided on the platen roller 105 is fit and which holds the recording paper 101 by thrusting it onto the platen roller 105, 107 expresses the L-shaped member which is joined together with the clamper 106 at the point P and is installed in such a manner as to permit its free rotating motion round the rotating shaft as the center of the motion, 108 represents the pin provided on the other end of the L-shaped member 107, 109 represents the twisting spring suspended between the clamper 106 and the L-shaped member 107 and used for thrusting under pressure the clamper 106 onto the platen roller 105, 111 indicates the thermal printing head for printing images on the recording paper 101,112 denotes the ink sheet which is formed of a transparent film with ink coated thereon to be stuck to the recording paper 101 through the sublimation of the ink by the heat generated by the thermal printing head 103,113 marks the ink sheet feeding reel which feeds the ink sheet 112, and 114 designates the take-up reel for winding up the ink sheet 112.
With this conventional printer, the platen roller 105 first turns in the direction indicated by the dotted line, as shown in FIG. 7, and the pin 108 thereby comes into direct contact with the hook 110. By the further rotating motion of the platen roller 105 in the same direction, the L-shaped member 107 moves in rotating motion around the point O as the center of its rotation, thereby lifting up the clamper 106 from the platen roller 5.
Next, the paper feeding roller 106 rotates in the direction along the arrow mark in a solid line, thereby transporting the recording paper 101 and inserting the paper between the clamper 106 and the platen roller 105.
Then, the platen roller 105 moves in its rotating motion in the direction indicated by the arrow mark in a solid line, and the clamper 106 is thereby moved downward, clamping the recording paper 101 and winding the paper as it is round the platen roller 105 as illustrated in FIG. 8.
FIG. 8 represents the modes for the printing of images. The ink sheet is heated, at the same time as it is thrust down under pressure onto the recording paper 101, by the thermal printing head 111. In the meantime, the platen roller 105 rotates in the direction indicated by the arrow mark in a solid line, and thereupon the ink of the ink sheet 112 as sublimated by the thermal printing head 111 is attached to the recording paper 101. With this process being performed three times, i.e. for each of the three colors, yellow magenta, and cyan, in the regular sequence, images are printed in color. Moreover, the thermal printing head 111 temporarily escapes in the upward direction when the clamper 106 passes the position of the thermal printing head 111, so that the thermal printing head 111 will not get into any direct contact with the clamper 106. Moreover, the hook 110 is so constructed that it escapes into the area on the outside of the rotating orbit of the pin 108, by the action of a driving mechanism not shown in the Figure, so that the hook will not come into any direct contact with the pin 108, when the platen roller 105 moves in its forward rotation, i.e. in the direction shown by the arrow mark in a a solid line.
FIG. 9 illustrates the state of the discharging of paper. After the images are printed in the three colors, the platen roller 105 moves in its reverse rotation in the direction shown by the arrow mark in a dotted line, and the recording paper 101 is thereby guided by the paper guide 104, and the recording paper 101 is discharged with the paper discharging roller 103 rotating in the direction shown by the arrow mark in a solid line. Also, with the reverse rotation of the platen roller 105, the pin 108 comes into its direct contact with the hook 110, and the clamper 106 is thereby lifted upward, releasing the clamp on the recording paper 101, so that the recording paper 101 continues to be transported forward with the paper discharging roller 103 to be discharged out of the printer.
Now that this conventional printer is constructed in such a manner as described above, it is necessary for the printer to turn its platen roller in reverse in order to feed the recording paper or to discharge the paper, with the result that the conventional printer is liable to the problem that the sequence of operations in it is made more complicated and that the printer does not permit any free setting of the paper pass because its paper feeding point and its paper discharging point are identical. This conventional printer is liable also to the problem that it tends to cause a jam of the recording paper while the paper is being transported from the clamper releasing position to the paper discharging paper because the printer performs the discharging of the recording paper by transporting the recording paper to the paper discharging roller while the paper is in the state of being released from the clamper.
FIG. 10 is a configuration chart illustrating a third conventional printer (for example, the printer according to Japanese Patent Application No. 173597-1986).
In this Figure, 201 indicates the recording paper, 202 stands for the clamper, 203 represents a platen roller in a cylindrical shape with an outer circumference somewhat longer than the length of the recording paper 201 mentioned above, and this platen roller takes up around itself the above-mentioned recording paper 201 with its top end secured by the clamper 202 mentioned above. 204 marks the ink sheet, and, on the surface of this ink sheet facing the recording paper 201 mentioned above, sublimatable ink is coated separately in regular sequence for each of the colors, yellow, magenta, and cyan, on its every recording unit area for one screen. 204a represents an ink sheet feeding reel around which the ink sheet 204 mentioned above is wound, and this ink sheet feeding reel constantly applies an adequate amount of back tension to the ink sheet 204 mentioned above for the transport of the paper in the direction indicated by the arrow mark. 204b denotes an ink sheet take-up reel, which rotates in such a way as to wind the ink sheet round itself. 205 indicates a line-type thermal printing head with heat generating elements 205a arranged thereon in a single line in the direction of the width of the recording paper 201 mentioned above. 206 and 107 are guide rollers for guiding the ink sheet 204 mentioned above, and these guide rollers are supported by the same supporting member (not illustrated in the Figure) as the thermal printing head 205 mentioned above. 208 represents a motor, which has a motor shaft 208a as its rotating shaft and works as the driving means for rotating the platen roller 203 mentioned above. 209 stands for a gear shaft. 210 represents a driving gear mounted axially on the motor shaft 208a mentioned above, and 211 represents a platen gear mounted axially on the platen shaft 203a mentioned above. 212 indicates an intermediate gear, which is supported in such a manner as to permit its free rotating motion round the gear shaft 209 mentioned above as the center of its rotation and kept in its constant meshing with the driving gear 210 mentioned above. 213 indicates an intermediate gear, which is supported in such a manner as to permit its free rotating motion round the gear shaft 209 mentioned above as the center of its rotation and kept in its constant meshing with the platen gear 211 mentioned above. The intermediate gears 212 and 213 mentioned above rotate together as one unified set. The modules for all of the driving gear 210 mentioned above, the intermediate gears 212 and 213 mentioned above, and the platen gear 211 mentioned above are identical, and these four gears form the speed reduction, driving, and transmission mechanism. The number of teeth, for example, is 22 on the driving gear 210 mentioned above, 88 on the intermediate gear 212 mentioned above, 59 on the intermediate gear 213 mentioned above, and 118 on the platen gear 211 mentioned above. Here, on the basis of the understanding that the speed reduction ratio means the number of rotations required of the gear at the driving side to make the driven gear rotate by one turn, the speed reduction ratio between the driving gear 210 mentioned above and the intermediate gear 212 mentioned above is 4, and the speed reduction ratio between the intermediate gear 213 mentioned above and the platen gear 211 mentioned above is 2, and the final speed reduction ratio of this speed reduction, driving, and transmission mechanism is 8.
Now, with reference to FIG. 11 through FIG. 13, a description is made of the operations of this third conventional printer, which has a construction described above.
First, the state of the feeding of paper is illustrated in FIG. 11, in which the thermal printing head 205 and the guide rollers 206 and 207 are aloof from the platen roller 203, and, when the clamper 202 is in the position on the platen roller 203 as shown in FIG. 11, the recording paper 201 is transported in the direction indicated by the arrow mark b, and the clamper 202 moves in the direction marked by the arrow mark c, holding the top end of the recording paper 201.
Then, the rotating power of the motor 208 is transmitted to the platen gear 211 by way of the driving gear 210 and the intermediate gears 212 and 213, and, as the result, the platen roller turns in the direction indicated by the arrow mark d, and, when the top end of the recording paper 201 comes to the specified recording start position in the proximity of the thermal printing head 205, the rotation of the motor 208 stops, upon which the rotation of the platen roller 203 comes to a temporary stop. At this moment, the area of the recording paper 201 proper for the starting of the registration of the yellow ink, which is the first color, has come to the position where the ink sheet 204 faces the heat generating element 205a. Thereupon, the thermal printing head 205 and the guide rollers 206 and 207 shift their positions in the direction shown by the arrow mark e, and the heat generating element 205a is brought into pressure contact with the platen roller 203, with the ink sheet 204 and the recording paper 203 intervening between them. This state is the state for the start of the recording operations and is shown in FIG. 12.
Next, the platen roller 203 rotates in the direction shown by the arrow mark f, and the recording paper 201 and the ink sheet 204, as kept in close contact with each other, are transported in the direction indicated by the arrow mark f, and, at the same time, the signals for the images in yellow are transmitted to the thermal printing head 205 in synchronization with the speed for the transport of the recording paper 201, the heat generating elements 205a being thereupon caused selectively to generate heat in regular sequence and to transfer the yellow ink onto the recording paper 201, thereby recording the images in yellow. In the course of this operation, the ink sheet feeding reel 204a rotates in the direction shown by the arrow mark h, giving adequate back tension to the ink sheet while the ink sheet take-up reel 204b rotates in the direction shown by the arrow mark i, winding the ink sheet 204 around itself. When the recording of the images in yellow is finished by the operations described above, the platen roller 203 comes to a temporary stop of its rotation, and the thermal printing head 205 and the guide rollers 206 and 207 shift in the direction as indicated by the arrow mark j, thereby moving away from the platen roller 203. This state is shown in FIG. 13 as the state of the completion of the recording operation.
Thereafter, the platen roller 203 rotates in the direction shown by the arrow mark k, and, when the top end of the recording paper 201 comes again to the same position as that for the start of the recording of the images in yellow, the platen roller 203 temporarily stops its rotation. In the meantime, the ink sheet 204 is transported by the ink sheet take-up reel 204b in the direction indicated by the arrow mark i for a certain prescribed duration of time, and, when the area for the start of the recording of the magenta ink, which is the second color, thus comes to the position facing the heat generating element 205a, the ink sheet take-up reel 204b stops its rotation.
After all the operations mentioned above with reference to FIG. 13 are completed, the thermal printing head 205 and the guide rollers 206 and 207 move in the direction indicated by the arrow mark m, and the heat generating element 205a is brought into pressure contact with the platen roller 203, with the ink sheet 204 and the recording paper 201 intervening between them. Thereupon, the platen roller 203 rotates, with which the images in magenta are recorded in overlapping with the yellow images already recorded on the paper. When the recording of the images in magenta is thus completed, the images in cyan are recorded in the same manner in overlapping with the already finished images, and the recording of the images in color is thereby completed.
In this regard, if there is any lack of uniformity in the pitch or any eccentricity in the pitch circle or the like in at least one gear among the driving gear 210, the intermediate gears 212 and 213, and the platen gear 211, the platen roller 203 will be prone to fluctuations in its rotation even if the motor 208 itself attains a favorable degree of precision in its revolution. Consequently, there occurs a lack of uniformity in pitch on the images as recorded on the recording paper 201. However, the configuration of the gears being such as described above, the intermediate gears 213 and 212 rotate two turns, and the driving gear 210 rotates eight turns, while the platen gear 211 rotates one turn. Therefore, the lack of uniformity in the rotation of the platen roller 203, resulting from such factors as the lack of uniformity in pitch or the eccentricity of pitch circle present in the individual gears, occurs in a cyclical period for each rotation of the platen roller 203. Hence, the relative positions in the relations for the meshing of the individual gears in the course of the recording of the images in yellow, for example, will occur again at the time when the images are recorded in magenta and also at the time when the images are recorded in cyan. As a result, the lack of uniformity in pitch as expressed in the recorded images will be the same for each of the colors, and this achieves a reduction in the deviation of the recorded colors.
In general, the execution of the recording of images in color in high picture quality requires the transfer of a plural number of pigments in duplication onto the same area on the paper, and the precision of this duplication gives considerable influence on the picture quality of the recorded images. If there are any deviations in the relative positions among the images recorded in the individual colors after the transfer of the ink, the so-called color deviation occurs, with the result that the recorded images are accompanied with unnatural color contours and are also affected by a deterioration in the resolution.
However, if an arbitrarily selected speed reduction ratio is set for the individual gears forming the speed reduction, driving, and transmission mechanism, which works to reduce the revolutions of the driving means and to transmit the reduced revolutions to the platen roller, in such a printer as just described, the relations in terms of the relative positions in the meshing of the individual gears at a given point in time in the course of one rotation of the platen roller will be different in some cases from the relative positions in the meshing of the individual gears in the course of the recording of the images in another color. In such a case, the characteristics of the unique irregularity in the revolutions of the individual gears will give different influences for the different colors to the irregularity in the revolutions of the platen roller, and such differences will result in causing deviation of color.
Consequently, it is in practice, as is the case with this type of conventional printer, to employ a method whereby the speed reduction ratios are set in integral numbers for all the individual gears comprising the speed reduction, driving, and transmission mechanism. This makes the relative positions in the relationship of the meshing among the individual gears identical for all the individual colors at any given point in time in the course of one rotation of the platen roller. Thus the fluctuations which occur in the rotation of the platen roller because of the intrinsic lack of uniformity in the rotation of the individual gears are made identical for all the individual colors, and the deviation of color is thereby reduced.
However, in case the relative positions in the relationship of the meshing among the individual gears are made identical as just described, each of the gears will get into contact with the other individual gears adjacent to it on their teeth in the same parts in every cycle of their rotation, with the result that the teeth in those parts will wear out more readily. In general, this kind of wear does not occur uniformly on all parts of the individual gears, but occur in some parts of the gears, causing a deviation of wear on the individual gears. This phenomenon presents the problem that, not only are fluctuations in the rotation of the platen roller, but the service life of the individual is shortened very considerably. In view of this problem, it can be pointed out that it is a deviation from the essentially proper designing concept to set in integral numbers all the speed reduction ratios of the individual gears forming the speed reduction, driving, and transmission mechanism.
FIG. 14 is a perspective view illustrating the construction of a fourth conventional printer, and FIG. 15 is a perspective view showing the construction of the paper discharging mechanism. In these Figures, 301 represents a paper cassette for storing the recording paper, 302 indicates the recording paper stored in the inside of this paper cassette, 303 denotes the platen roller around which the recording paper 302 is wound at the time of transferring the images, 304 shows a clamper set for its free movement in the direction R of the radius of the platen roller 303 mentioned above, and 305 marks the thermal printing head which performs the transfer of images onto the recording paper 302. 306 indicates the motor, and the revolutions of this motor are transmitted from the output gear 307, which is installed on the output shaft of the motor, to the gear 308 and then from the gear 310, which is mounted coaxially with this gear 308, to the gear 310, which is mounted on the rotating shaft 311 of the platen roller 303 mentioned above. Thus, the revolutions of the motor so transmitted drive the platen roller 303 for its rotating motion. 312 shows the paper feeding roller which feeds the recording paper 302 mentioned above towards the platen roller 303, and 313 indicates the paper discharging roller which discharges the recording paper 302 on which the transfer of images has been completed. 314 represents an ink sheet, which is stored inside the ink cassette not shown in the Figures but stored inside the ink cassette. Ink sheet 314 is made of transparent film coated with ink. 315 indicates the paper detecting sensor. 316 shows the upper cover for the paper discharging mechanism, and 318 shows a slider which pushes the recording paper 302 to the front face of the printer. 319 represents the optical sensor which detects the recording paper 302 upon its arrival at the prescribed position in the paper discharging mechanism.
Next, the operations are explained with reference to FIG. 16 through FIG. 22. FIG. 16 shows the state of paper feeding. With the paper feeding roller 312 rotating in the direction shown by the arrow mark a, the recording paper 302 is transported forward and passes through the position of the paper detecting sensor 315. Then, the paper detecting sensor 315 detects the passage of the recording paper 302 and generates a signal as shown in FIG. 19. After approximately A seconds after this paper detecting sensor 315 generates the signal, the recording paper 302 is inserted between the clamper 304 and the platen roller 303. The clamper 304 moves in the direction R.sub.l towards the center of the platen roller 303, after the above-mentioned A seconds after the paper detecting sensor 315 generates the signal, and holds the recording paper 302 on the platen roller 303 by applying pressure to the paper. Subsequently, the motor 306 revolves, and its motion is transmitted to the platen roller 303 via the gear 307, the gear 308, the gear 309, and the gear 310, and, with the rotation of the platen roller 303 in the direction shown by the arrow mark b, the recording paper 302 is wound around the outer circumference of the platen roller 303.
FIG. 17 illustrates the state of the transfer of images. The ink sheet 314 is pressed against the recording paper 302 by the thermal printing head 305, and, at the same time as the platen roller 303 rotates in the direction shown by the arrow mark b1 in the Figure, the thermal printing head 305 generates heat, by which the ink on the ink sheet 314 is sublimated and stuck on the recording paper 302. The printer executes the printing of images in color on the recording paper 302 by performing the fixing of the ink in this manner for each of the three colors, yellow, magenta, and cyan. The transfer of images in each of these colors is started at the moment when the photoelectric switch 316 has detected the clamper 304.
Moreover, when the clamper 304 rotates, passing through the position of the thermal printing head 305, the thermal printing head temporarily evacuates upwards lest it should interfere with the movement of the clamper 304.
FIG. 18 shows the state of the discharge of the recording paper. After the completion of the transfer of the images in three colors, the platen roller 303 moves in reverse in the direction shown by the arrow mark c in the Figure, and the recording paper 302 is then guided by the paper discharging guides are not shown in the Figure and is transported to the paper discharging mechanism by the paper discharging roller 313. While this operation is being performed, the slider 318 is in its home position as shown in FIG. 20. When the recording paper 302 comes to the prescribed position in the paper discharging mechanism as shown in FIG. 21, the optical sensor 319 detects the recording paper 302. Receiving a signal on the detection of the paper thus generated by the optical sensor 319, the slider 318 shifts its position in the direction A by means of the driving mechanism not shown in the Figure, pushing the paper in the direction A. The recording paper 302 pops out of the front panel not illustrated in the Figure, when the slider 318 has moved to the second position as shown in FIG. 22, and the paper discharging operation is finished thereupon. When the discharging of the paper is thus finished, the slider 318 moves in the direction B, returning to its home position.
The conventional printer is constructed as described above. As static electricity is generated on the recording paper after the transfer of images onto it, the recording paper 302 may sometimes be stuck to the upper cover of the paper discharging mechanism, in which case it is highly probable that a jam of the paper will occur. Furthermore, the conventional printer is to the problem that its construction causes considerable difficulty in removing jammed paper from inside its paper discharging mechanism.
FIG. 23 is a perspective view illustrating the construction and operations of the paper discharging mechanism installed in a fifth type of conventional printer.
In this Figure, 401 represents the recording paper, 402 marks the guide, which has a slope 402a as illustrated in the said Figure. 403a and 403b are transporting rollers forming a pair and provided in the upper and lower positions respectively, and these rollers are supported in a manner permitting their free rotating motion in the positions shown in the Figure. The transporting roller 403a mentioned above is given its force to work on the transporting roller 403b mentioned above by a force providing means not shown in the Figure. 404 indicates a motor, which works as the driving means for the transporting roller 403b mentioned above, and the pulley 406, which is fixed on the shaft of the motor 404 mentioned above, and 406 is a pulley fixed on the shaft of the above-mentioned transporting roller 403b. 407 is a wire, which is the means of transmitting the revolving force of the motor 404 from the pulley 405 mentioned above to the pulley 406 mentioned above. 408 is the upper cover for the above-mentioned guide 402.
Next, a description is made of the paper discharging mechanism in this fifth type of conventional printer constructed as mentioned above.
The revolving power of the motor 404 is transmitted to the transporting roller 403b by way of the pulley 405, the wire 407, and the pulley 406, and, as the result of this transmission of the power, the transporting rollers 403a and 403b rotate respectively in the direction shown by the arrow mark a and the direction shown by the arrow mark b. In this state, the forward end of the recording paper 401 is put between the transporting rollers 403a and 403b, and the recording paper 401 is transported forward in the direction shown by the arrow mark c, being thereby pushed out onto the slope 402a.
When the recording paper 401 is thus pushed out to the full extent by the transporting rollers 403a and 403b, the recording paper 401 is released from the capture by the above-mentioned transporting rollers 403a and 403b, so that the paper glides down the slope 402a mentioned above to be delivered out of the lower area of the guide 402.
As described so far, the conventional paper discharging mechanism occasionally fails to discharge the paper with certainty since the recording paper sometimes does not slide well over the slope because of a difference in the coefficient of friction between the recording paper and the surface of the slope or since the recording paper sometimes sticks to the slope in consequence of static electricity generated thereon.
Therefore, a discharging mechanism, which operates with a separately provided discharging block, is employed to apply the driving force to discharge the recording paper as pushed out onto the guide by the transporting rollers.
However, even if the discharging block is put into operation only after a certain duration of time has passed after the recording paper is fed into the transporting rollers, without first ascertaining whether or not the recording paper has been fully released from the transporting rollers, the mechanism is liable to make an error in its operation in that the paper discharging block may set into its operation although the recording paper is not yet fully released, on account of various factors, from its engagement in the transporting rollers. Also, a jam of paper may occur as the result of the capture of the fringe of the paper in the guide or the upper cover in consequence of the skew of the recording paper at the time when the paper discharging block is put into its operation.
FIG. 24 and FIG. 26 illustrate one example of the paper transporting method incorporated in a sixth color thermal printer. In these Figures, 501 indicates the recording paper on which information is to be transferred in the form of printed images, 501 marks the clamper which grips and transports the recording paper 501, and 503 represents the platen roller for winding the recording paper 501 around it and for transporting the recording paper 501 and the ink sheet. 504 indicates an ink sheet, which places color on the recording paper 501, and 505 shows the roller for transporting the ink sheet. 506 marks the thermal printing head, which performs the transfer of images to the recording paper 501 by putting the ink sheet 504 against the paper and applying heat to the said ink sheet. 507a and 507b show the paper feeding rollers, which transport the recording paper 501 from an outside area into the printer mechanism. 508a and 508b indicate the paper discharging rollers, which transport the recording paper 501 to the outside area.
Moreover, FIG. 30 illustrates the color pattern for one image screen area, and, in this pattern, 510 shows the area for Y (yellow), 511 shows the area for M (magenta), and 513 shows the area for C (cyan). 515a and 515b represent the detecting part of the sensor.
Next, a description is made of the operations of the equipment.
First, FIG. 24 shows the state of paper feeding. The recording paper 501 is transported by the paper feeding rollers 507a and 507b to move forward to the clamper 502. At this point, the clamper, which has been open to the outside, closes toward the inner area, clamping the fore end of the recording paper 501. Now, the platen roller 503 begins its rotation in the counterclockwise direction, winding the recording paper 501 around the platen roller 503. When the roller has rotated by approximately three fourths of one rotation, the thermal printing head 506 comes down by rotation and puts the ink sheet 504 into close contact with the recording paper 501 wound around the platen roller 503. Also, heat is applied to the heater line of the thermal printing head, and the ink from the Y (yellow) sheet is first transferred to the recording paper 501 with the rotation of the platen roller 503. When the transfer of images in Y (yellow) is finished, the thermal printing head 506 temporarily shifts its position upward in order that it will not interfere with the passage of the clamper 502, and, when the clamper 502 finishes its passage, the thermal printing head 506 moves down as shown in FIG. 25, and the ink in M (magenta) is transferred this time from the ink sheet 504 to print the images in the same manner as in the transfer of Y (yellow). When the thermal printing head 506 comes down after the passage of the clamper 502 after the completion of the transfer of the images in M (magenta), the clamper operates to form the state of its opening to the outside, as shown in FIG. 27, and, as the images continue to be printed in the final color, C (cyan), with the ink applied from the ink sheet 504, the recording paper 501 arrives at the paper discharging rollers 508a and 508b, and the recording paper is transported to the outside area by the rotation of the rollers.
As described above, a color print obtained by transferring the three colors, Y, M, and C, in overlapping from the ink sheet 504 onto the recording paper with the rotation of the ink sheet feeding roller 505a and the ink sheet take-up roller 505b as shown in FIG. 28. In this regard, FIG. 29 and FIG. 28 illustrate the state with the case for the ink sheet removed.
As mentioned above, it is necessary with the ink sheet on this color thermal printer to perform the discharge of the paper by opening the clamper 502 at the time when the images are to be printed in C (cyan) at the final ink transferring process. Thus, the recording paper 501, which has become free at the time of its discharge fails to move forward together with the ink sheet 504 in the course of the transfer of images onto it because of the resistance the paper receives from the guide, etc., and this lag in the movement of the paper works as a factor causing such defects as a deviation of color.